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Web services are a way to connect different systems and exchange information
among them, specific information on specific circumstances, for instance, a
crm tool with an ERP, or an specific DB to deposit new information or
consult a current one.

If you have a Sales force CRM, you might need to read information from other
systems or well, feed with new information other systems.

Regarding how to use them, I strongly recommend you to find SME to support
you in the task you need to complete, I believe general steps aren't going
to solve your issue.
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